Mechanical foam generating method and system

ABSTRACT

A first portion of water under pressure is mixed with a foam liquid concentrate and a gas such as air in a pump to form a primary foam upon discharge from the pump and a second portion of water under pressure is mixed with the primary foam thereby enabling the generation of a given volume of foam by the use of a smaller pump than would be required by the prior practice of passing both portions of water through the pump.

United States Patent [191 Williamson [11] 3,846,515 [451 Nov. 5,1974

[ MECHANICAL FOAM GENERATING METHOD AND SYSTEM [75] Inventor: Hilding V.Williamson, Highland Park, 111.

[73] Assignee: Chemetron Corporation, Chicago,

22 Filed: Sept. 17, 1973 21 Appl. No.: 398,138

Related US. Application Data [63] Continuation of Ser. No. 170,786, Aug.11, 1971,

abandoned.

[52] US. Cl. 261/18 B, 169/15, 261/28, 26l/D1G. 26 [51] Int. Cl130113/04 [58] Field of Search 169/15; 261/DIG. 26, 18 B, 261/28 [56]References Cited UNITED STATES PATENTS 1,749,411 3/1930 Burmeister169/15 1,977,171 10/1934 Clithero et a1... 169/15 X 2,164,153 6/1939Friedrich 261/D1G. 26 2,201,040 5/1940 Hansen-Ellehammer.... 261/DlG. 262,249,095 7/1941 Swift et al 261/D1G. 26

2,307,082 1/1943 Te Grotenhuis 261/D1G. 26 2,543,941 3/1951 Sargent169/15 3,234,962 2/1966 Williamson 137/565 3,353,550 11/1967 Williamson137/114 3,620,306 11/1971 Shepherd 26l/D1G. 26 FOREIGN PATENTS ORAPPLICATIONS 314,975 2/1934 Italy 261/D1G. 26 426,513 4/1935 GreatBritain 261/D1G. 26 689,818 4/1953 Great Britain... 261/28 872,0022/1953 Germany 261/D1G. 26 910,744 3/1954 Germany 169/15 PrimaryExaminer-Tim R. Miles Assistant ExaminerRichard L. Chiesa Attorney,Agent, or Firm-N. M. Esser [5 7] ABSTRACT A first portion of water underpressure is mixed with a foam liquid concentrate and a gas such as airin a pump to form a primary foam upon discharge from the pump and asecond portion of water under pressure is mixed with the primary foamthereby enabling the generation of a given volume of foam by the use ofa smaller pump than would be required by the prior practice of passingboth portions of water through the pump.

16 Claims, 2 Drawing Figures MECHANICAL FOAM GENERATHNG METHOD ANDSYSTEM This is a continuation of application Scr. No. l70,786 filed Aug.11, l97l and now abandoned.

This invention relates generally to a mechanical foam generating methodand a system incorporating that method. It relates particularly to amethod of operating an in-line foam pump system in which a foam liquidconcentrate and a diluent such as water are mixed with a gaseous mediumsuch as air in a rotary positive displacement type pump, to form a foamupon discharge from the pump. it relates more particularly to a systemin which only aportion of the diluent is passed through the pump, theremainder being mixed with a concentrate-rich foam at a point downstreamfrom the pump.

The foam generated by the system of this invention is generally calledmechanical foam by those skilled in the art to distinguish it from foamproduced by gasgenerating chemical reactions, which is called chemicalfoam." Mechanical foam in which the gaseous medium is air is called airfoam.

Mechanical foam is used to extinguish fires, to blanket structures andequipment so that heat radiation therefrom is diminished, to blanketliquids and other materials so that the generation of flammable or toxicvapors is diminished, to fill rooms and other enclosures whereinflammable or toxic vapors might otherwise collect, to blanket airportrunways so that the friction spark hazard is reduced when an aircraftmust land on its airframe, and to act as an insulating medium in manyother situations.

As indicated in Section 17, Chapter III of Fire Protection Handbook"(National Fire Protection Association, Boston, 1969, 13th edition)in-line foam pump systems are among the basic types of mechanical foamgenerating systems used. In systems of this type known in the art priorto this invention the entire charge of water present in the foamgenerated had to pass through the pump. The conventional mechanical foamgenerating systems designed to produce foams having a low expansionratio (i.e., about 30:] or less) but in systems comprising a rotarysliding vane pump it is not desirable to pass enough water through thepump to give a foam having an expansion ratio less than about l2:l atthe maximum delivery rate of the pump. The expansion ratio of a foamdelivered at the maximum delivery rate of the pump within the system isdependent upon the liquid capacity of the pump since the expansion ratiois defined as the ratio ofthe volume ofthe foam to the volume of liquidspresent therein. Thus, a pump having a delivery rate of about 6,000gallons per minute (g.p.m.) of foam having an expansion ratio of 12:1has a liquid capacity of about 500 g.p.m.

The load placed on the pump and the drive means therefor by a largeliquid throughput requires the use of large pumps with heavilyconstructed components and a drive means having a high horsepowerrating, all of which adds greatly to the cost of the system. The dangerof breaking the pump under such loads is a further disadvantage ofpriorart systems designed to generate low expansion foam.

It is a principal object of this invention, therefore, to provide animproved method of generating mechanical foam and a system incorporatingthat method.

It is a further object of this invention to provide a mechanical foamgenerating methodand system wherein water, a foam liquid concentrate,and a gas, such as air, are mixed in a rotary positive displacement pumpto form a foam upon discharge therefrom and additional water is mixedwith the foam at a point in the system beyond the discharge port of thepump.

It is another object of this invention to provide a method and systemfor proportioning the amounts of foam liquid concentrate and water to bemixed in the pump.

That these and other objects are fulfilled by this invention will beevident from the following description.

It has been found that a mechanical foam having a lower expansion ratiothan previously possible from conventional mechanical foam systemscomprising a rotary sliding vane pump operating at maximum capacity maybe generated by a system wherein only a portion of the water required tomake the desired foam is passed through a foam pump along with the foamliquid concentrate and a gas such as air, the remainder being by-passedaround the pump to mix with the foam formed upon discharge of theconcentrate-rich mixture from the pump.

The mechanical foam generating system of this invention comprises a pumphaving a gas inlet port, a liquid inlet port and a foam outlet port, aliquid inlet conduit connected to the liquid inlet port, a main waterconduit adapted for connection to a source of water under pressure, apump water conduit between the main water conduit and the liquid inletconduit, a foam liquid concentrate conduit adapted for connection to aconcentrate reservoir and connected to the liquid inlet conduit, a foamconduit connected to the foam outlet port and a by-pass water conduitbetween the main water conduit and the foam conduit whereby a portion ofthe water by-passes the foam pump.

The method of this invention comprises the steps of dividing a stream ofwater under pressure into first and second portions, mixing the firstportion of the water with a foam liquid concentrate and a gas in arotary positive displacement pump to make a concentraterich mixture,discharging said mixture from the pump to made a primary foam, andmixing the second portion of water with the primary foam to make adiluted foam. The diluted foam is a mechanical foam having an expansionratio between about 15:] and about 2:] or less. For most applicationsthe ratio will be between about 4:1 and about 12:1.

The stream of water may be obtained from any suitable source as long asthe water is under pressure at the point where it enters the system. Thesource may be a municipal water supply or a separate water reservoir. Inthe latter case the pressure may be created by raising the reservoir toa suitable height above the system or by pumping the water to the systemby means of a centrifugal pump or the like.

The relative sizes of the first and second portions into which thestream of water is divided will be determined by the capacity of therotary positive displacement pump (i.e., the foam pump) in the foamgenerating sys I tem, the amount of cooling required for the pump, the

concentration of the foam liquid concentrate and the v expansion ratiodesired. Usually the second portion will constitute the major portionbut in cases where the capacity of the foam pump is only slightly lessthan that required to deliver a given volume of foam having a givenexpansion ratio the first portion may be the major one. It follows thatthe two portions of water may be of equal volume. Most often the secondportion will be from about 60 to about 90 percent, preferably from about70 to 80 percent of the total volume of water. The water, and foamliquid concentrate, however, act as a coolant for the pump so that thepump will operate at or near isothermal conditions. To effect thenecessary cooling the mixture of water and concentrate pass ing throughthe pump is usually at least about 40 percent of the liquid capacity ofthe pump.

The foam liquid concentrate may be any one of the known productscommonly used for the generation of mechanical foam. These include theprotein and synthetic types. The fluorinated surfactants and thedetergents are examples of the latter type.

The gas used in mechanical foam generation is commonly air since it isthe most available one. Other nonflammable gases such as nitrogen mayalso be used, however.

The proportions of the concentrate and the first portion of water aresuch that the primary foam will contain all of the concentrate whichwill be present in the diluted foam. The conventional concentrates aredesignated as 3 percent and 6 percent concentrates which means that theyare used in proportions of 3 percent and 6 percent by volume.

The rotary positive displacement type pump used as the foam pump in thismethod is usually of the rotary sliding vane type as described in US.Pat. Nos. 3,353,550; 3,234,962, and 2,827,858, which are herebyincorporated by reference into this disclosure. Other rotary positivedisplacement type pumps may also be used.

The primary or concentrate-rich foam is formed as the concentrate-richmixture is discharged from the pump into a conduit attached to the pump.This conduit serves as a mixing chamber when the second portion of wateris introduced into the conduit at a point downstream from the point ofdischarge from the pump.

The foam resulting from the mixture of the second portion of water withthe primary foam is a diluted foam and has an expansion ratio less thanthat of the primary foam. The reduction in the expansion ratio isdetermined by the amount of water added to the primary foam. Forexample, in 6,000 gallons of foam having an expansion ratio of 6 thetotal volume of liquid is 1,000 gallons, of which 60 gallons will be 6percent foam liquid concentrate. To make 6,000 g.p.m. of foam, the 940g.p.m. of water is divided into a first portion of 188 g.p.m. percent)and a second portion of 752 g.p.m. (80 percent). The primary foam formedby mixing the first portion of water with 60 g.p.m. of foam liquidconcentrate and 5,000 g.p.m. of air will have an expansion ratio of5248/248 or about 21:1. A primary foam generated from 464 g.p.m. ofwater, 36 g.p.m. of6 percent concentrate and 5,500 g.p.m. of air willhave an expansion ratio of 12. Adding 100 g.p.m. to the primary foamwill give a foam having an expansion ratio of about 101:].

The mixing of the second portion of water with the primary foam may takeplace in an open, unobstructed conduit or, at least partially, in a foamrefiner comprising a screen or series of screens or a bundle of paralleltubes inserted in the conduit. The axes of the tubes are parallel to theaxis of the conduit. A laminar flow is more conducive to the formationof substantially uniform bubbles and in applications whereasubstantially homogeneous foam is desired the mixing of the dilutedfoam may include a refining step. In order to avoid too great a pressuredrop during the refining step the crosssectional flow area of the foamrefiner should be at least equal to that of the conduit carrying thefoam.

The system incorporating the method of this invention will be betterunderstood from the following descriptions with reference to thedrawings.

FIG. 1 illustrates a fire truck equipped with a foam generating systemof this invention.

FIG. 2 is a semi-diagrammatic view showing an embodiment of thisinvention suitable for a stationary installation.

In FIG. 1 truck chassis 10 supports foam liquid concentrate reservoir 11upon which is mounted pump 12 driven by a power take-off from the truckengine, a separate diesel engine, or the like. Pump 12 has air inletport 13 and liquid inlet port 14 which is connected to liquid inletconduit 15 which is connected to foam liquid concentrate conduit 16, inwhich valve 17 is interposed, and to pump water conduit 18, in whichvalve 19 is interposed. Conduit 18 is connected to main water conduit 20at a point upstream from valve 21 which controls the flow of water frommain conduit 20 to by-pass conduit 22. Main conduit 20 is adapted forconnection to a city water hydrant or other source of water underpressure. Flow rate indicator 23 is interposed between main conduit 20and by-pass conduit 22.

Foam conduit 24 is connected to outlet port 25 of pump 12 and to by-passconduit 22 and foam refiner 26. Distribution conduit 27 is connected tofoam refiner 26 and is adapted'to be connected to a discharge turret, asshown, or to some other discharge apparatus. Distribution conduit 27-may also be extended at its lower end and adapted for sub-surfaceapplication of the foam and for various other modes of application.

In operation foam liquid concentrate and water are drawn from reservoir11 and main water conduit 20, through conduits 16 and 18, respectively,by pump 12. The proportions of foam liquid concentrate and water areregulated by valves 17 and 19, respectively. Only a portion of the waterflowing through conduit 20 passes through pump 12, the amount beingregulated by valve 19. The concentrate and water mix in liquid inletconduit l5 and the mixture enters pump 12 through port 14. Air is drawnthrough port 13 into pump 12 wherein it is mixed with the concentrateand water. A foam rich in concentrate is formed as the mixture is forcedinto conduit 24 through port 25; The remainder of thewater flowingthrough conduit 20 by-passes pump 12 via conduit 22 and mixes with theconcentrate-rich foam in foam conduit 24 at the junction of conduit 22and conduit 24. The diluted foam may then pass through foam refiner 26wherein the bubbles comprising the foam are made uniformly small bypassage of the foam through a screen, a series of screens, or a bundleof parallel tubes which comprise refiner 26.

The diluted foam flows into distribution conduit 27 from which it maybedischarged through a nozzle or other means for application to thesubstance to be pro- V tected.

In FIG. 2, pump 40, mounted on a suitable support (not shown), ahdhaving a suitable drive means (also not shown), has air inlet 41. Liquidinlet port 42 of pump is connected to liquid inlet conduit 43 which isconnected to foam liquid concentrate conduit 44. An orifice plate orother flow-restricting means 45 is located in conduit 44 which isadapted for connection to a liquid foam concentrate reservoir (notshown). Conduit 44 is provided with automatic valve 46 and manualshut-off valve 47. Pump water conduit 48 is connected to inlet conduit43 and is provided with an orifice plate or other flow-restricting means49 and pressure reducing valve 50. Main water conduit 51 is connected topump water conduit 48 and is adapted for connection to a municipal waterhydrant or other source of water under pressure. Check valve 52 isinterposed between manual shut-off valves 53.

Outlet port 54 of pump 40 is connected to foam conduit 55 which isprovided with check valve 56 and is connected to bypass water conduit57. By-pass conduit 57 is connected to main water conduit 51 and isprovided with self-regulating valve 58 fitted with tubes 59 which areconnected to by-pass conduit 57 on either side of an orifice plate orother flowrestricting means 60. Distribution conduit 61 is connected tofoam conduit 55 and by-pass conduit 57 and may optionally be providedwith foam refining means 62 which may be a porous screen or series ofscreens or the like. Distribution conduit 61 is adapted for connectionto a suitable discharge means. Drain valve 63 is located at thelowermost point of the system, illustrated here as being at an elbow ofbypass conduit 57.

Optionally, foam conduit 55 may be fitted with pressure gauge 64 andvent conduit 65 which is equipped with pressure relief valve 66.

In operation the foam generating system illustrated in FIG. 2 differsfrom that of FIG. 1 in that it is adapted for automatic control of theliquid and foam flow. All manually operated shut-off valves, that is,valves 47 and 53, may normally be open.

The drive means for pump 40, in response to the stimulus of heat or atiming mechanism or the like, rotates the vanes ofpump 40 and therebycreates a partial vacuum in conduits 43, 44 and 48 and air inlet 41.This partial vacuum causes valves 46 and 50 to open, allowing foamliquid concentrate and a portion of the water under pressure in mainconduit 51 to be drawn into pump 40. The proportions of the concentrateand water are controlled by the pressure head on each and therestriction imposed on conduits 44 and 48, separately. At a givenpressure, the flow rates of each will be determined by the orifice sizein the respective conduits and thus the flow-restricting means may alsobe properly called proportioning means. Air is drawn into pump 40 as thevanes pass air inlet 41. The concentrate, water and air are mixed inpump 40 and a concentrate-rich foam is formed as the mixture is forcedinto foam conduit 55. This foam flows past check valve 52 into thejunction of conduits 55, 57 and 61. The pressure gradient created acrossorifice plate by this flow is transmitted to valve 58 by tubes 59,causing valve 58 to open and allow water to flow through bypass conduit57 and mix with the concentrate-rich foam. The diluted foam then flowsthrough distribution conduit 61 to a nozzle or other suitable dischargemeans. If desired, the diluted foam may be refined by passing it througha screen or other foam refining means 62 situated in conduit 61.

In the event pressure within foam conduit 55 exceeds a predeterminedvalue, pressure relief valve 66 opens to permit vent conduit to carrythe foam out of the system. The predetermined value is usually no higherthan about 50 p.s.i. but may vary according to the stresscharacteristics of the remainder of the system.

It should be understood that the foregoing description of the inventionis illustrative only and the scope of the invention should be determinedfrom the following claims.

I claim:

1. A mechanical foam generating system comprising a pump having a gasinlet port, a liquid inlet port and a foam outlet port, a liquid inletconduit connected to the liquid inlet port, a main water conduit adaptedfor connection to a source of water under pressure, a pump water conduitbetween the main water conduit and the liuqid inlet conduit, a foamliquid concentrate conduit adapted for connection to a concentratereservoir and connected to the liquid inlet conduit, a foam conduitconnected to the foam outlet port and a by-pass water conduit betweenthe main water conduit and the foam conduit whereby a portion of thewater by-passes the pump.

2. The system of claim 1 characterized further by means forproportioning the amounts of foam liquid concentrate and water flowinginto the pump.

3. The system of claim 2 wherein the proportioning means compriseorifice plates in the foam liquid concentrate and pump water conduits.

4. The system of claim 1 characterized further by a means for regulatingthe flow of water through the bypass water conduit.

5. The system of claim 4 wherein the regulating means comprises a valveresponsive to a pressure differential across a restriction in theby-pass water conduit.

6'. The system of claim 1 characterized further by means for relievingpressure in excess of a predetermined value in the foam conduit.

7. The system of claim 1 characterized further by a check valve mountedin the foam conduit and arranged to permit flow of foam away from thepump only.

8. The system of claim 1 characterized further by a check valve mountedin the main water conduit and arranged to permit flow of water to thepump water conduit and bypass water conduit and to check flow of foamfrom said conduits into the water source.

9. A method for generating mechanical foam comprising the steps ofdividing a stream of water under pressure into first and secondportions, mixing the first portion of the water with a foam liquidconcentrate and a gas in a positive displacement pump to make aconcentrate-rich mixture, discharging said mixture from the pump to forma primary foam, and mixing thesecond portion of water with the primaryfoam to make a diluted foam. t

10. The method of claim 9 wherein the first and second portions of waterare of equal volume.

11. The method of claim 9 wherein the second portion is a major portionof the water.

12. The method of claim 9 wherein the second portion constitutes fromabout 70 to about percent of the stream of water.

13. The method of claim 9 wherein the step of mixing the second portionof water with the primary foam in- 7 8 eludes refining of the dilutedfoam toamass ofsubstanis refined by passing it through a conduit havingits tially uniform bubbles. crosssection filled with tubes having axesparallel to 14. The method of claim 13 wherein the diluted foam eachother and'the conduit. is refined by passing it through at least onescreen. 16. The method of claim 9 wherein the gas is air.

15. The method of claim 13 wherein the diluted foam

1. A mechanical foam generating system comprising a pump having a gasinlet port, a liquid inlet port and a foam outlet port, a liquid inletconduit connected to the liquid inlet port, a main water conduit adaptedfor connection to a source of water under pressure, a pump water conduitbetween the main water conduit and the liuqid inlet conduit, a foamliquid concentrate conduit adapted for connection to a concentratereservoir and connected to the liquid inlet conduit, a foam conduitconnected to the foam outlet port and a by-pass water conduit betweenthe main water conduit and the foam conduit whereby a portion of thewater bypasses the pump.
 2. The system of claim 1 characterized furtherby means for proportioning the amounts of foam liquid concentrate andwater flowing into the pump.
 3. The system of claim 2 wherein theproportioning means comprise orifice plates in the foam liquidconcentrate anD pump water conduits.
 4. The system of claim 1characterized further by a means for regulating the flow of waterthrough the by-pass water conduit.
 5. The system of claim 4 wherein theregulating means comprises a valve responsive to a pressure differentialacross a restriction in the by-pass water conduit.
 6. The system ofclaim 1 characterized further by means for relieving pressure in excessof a predetermined value in the foam conduit.
 7. The system of claim 1characterized further by a check valve mounted in the foam conduit andarranged to permit flow of foam away from the pump only.
 8. The systemof claim 1 characterized further by a check valve mounted in the mainwater conduit and arranged to permit flow of water to the pump waterconduit and bypass water conduit and to check flow of foam from saidconduits into the water source.
 9. A method for generating mechanicalfoam comprising the steps of dividing a stream of water under pressureinto first and second portions, mixing the first portion of the waterwith a foam liquid concentrate and a gas in a positive displacement pumpto make a concentrate-rich mixture, discharging said mixture from thepump to form a primary foam, and mixing the second portion of water withthe primary foam to make a diluted foam.
 10. The method of claim 9wherein the first and second portions of water are of equal volume. 11.The method of claim 9 wherein the second portion is a major portion ofthe water.
 12. The method of claim 9 wherein the second portionconstitutes from about 70 to about 80 percent of the stream of water.13. The method of claim 9 wherein the step of mixing the second portionof water with the primary foam includes refining of the diluted foam toa mass of substantially uniform bubbles.
 14. The method of claim 13wherein the diluted foam is refined by passing it through at least onescreen.
 15. The method of claim 13 wherein the diluted foam is refinedby passing it through a conduit having its crosssection filled withtubes having axes parallel to each other and the conduit.
 16. The methodof claim 9 wherein the gas is air.